This invention relates to the method of inline forming of integral fasteners with film or sheet stock to be made into bags or other containers which are closable by the fastener elements. For a considerable period of time, bags with integral fasteners have been made by the blown film process similar to that taught in U.S. Pat. No. 3,340,116, for example. Here the fastening elements are extruded from the same polymer melt streams through an annular die containing the fastener extrusion orifices. Another technique for manufacturing such integral zippers is that taught, for example, in U.S. Pat. No. 3,462,332. This patent discloses a cast film process wherein the fastener elements are extruded separately from the film and are thereafter joined with the film by being brought together against a rotating cooling roll while the film and fastening elements are still in a fusible state.
While both the prior art blown film and cast film processes have produced commercial products, those made by the relatively faster cast film process have lacked certain advantages. The ability of fastener elements to resist rotation to obtain better interlocking remained a desired end. The ability to readily and controllably make thickened bases for the fastener elements yet maintain high production speeds, with the ability to make multiple and variable sized bags out of a single cast film, all remained a need until the present invention. While U.S. Pat. Nos. 3,198,228 and 3,338,284 show thickened bases, these are not found in a cast process. Also to be desired was to have cast die lips of sufficient thickness so as not to be susceptible to damage. The reliable high speed process for producing superior integral fastener elements taught by this invention meets the needs left unanswered by the prior art.